Conventionally, an illumination light guide has been known in which a plate-shaped or band-shaped light guide body is used in order to increase a light emitting area of a lamp. For example, Japanese Patent No. 5210061 discloses a light guide in which a plate-shaped light guide body is provided inside a lamp cover so as to cause the light of a light source to be incident from one end surface of the light guide body, and so as to guide the incident light in the longitudinal direction to be emitted to the outside from the entire surface area thereof.